Nanogenerators for Mechanical Energy Harvesting

Interview conducted by Stuart MilneJul 9 2015

Dr. Xudong Wang, Associate Professor in the department of Materials Science and Engineering at University of Wisconsin, talks to AZoNano about his research into nanogenerators used in vehicle applications for harvesting mechanical energy.

Can you please explain what a nanogenerator is?

The first Nanogenerator was developed in 2007 using piezoelectric nanostructures to harvest low-level mechanical energy. Its nanoscale building blocks enable higher sensitivity and higher efficiency compared to bulk structures. Now, the nanogenerator concept has been broadened to the principle of the triboelectric effect (i.e. triboelectric generator), where the contact between two dissimilar surfaces creates charge distribution, and thus inducing current flow externally.

Video Courtesy of Georgia Tech YouTube Channel

How has this been applied to your research?

The triboelectric effect has been applied in our research. In our design, we take the advantage of the contact between the tire and ground, which are regarded as two dissimilar materials to create charge separation. Our design allows immediate draining of the induced charge once the tire surface moves away from the ground. Continuously rolling of tires will continuously produce charge to the tire surface, which can thus generating continuous current pulses.

Wang and his colleagues used a toy car during initial trials. Courtesy of the College of Engineering

How is the power generated from these nanogenerators supplied to the vehicle to help reduce its reliance on the engine?

This type of generator directly outputs electric pulses in the form of AC, just like all the other types of triboelectric nanogenerators. This type of electric output can be regulated into a DC form to charge the car battery.

A car generates a lot of kinetic energy. Could this technology be applied in other areas of the vehicle?

There definitely is a possibility. But different moving parts may need specifically designed configurations to effectively harvest the energy. In addition, we don’t want to create any influence to the movement of these parts, such as increasing the friction, changing the mechanical property, etc.

Making vehicles more efficient is nothing new. How do you see this technology being incorporated into other new technologies such as the new engine recovery units we see in Formula 1?

We acknowledge all the other approaches to improve the fuel efficiency, but our technique is different from other approaches. The core of our concept is to recycle the energy that is otherwise and inevitably wasted. Therefore, the energy saved by our technology does not overlap with other energy efficiency improvement approaches. It is a net gain of energy efficiency.

Is there any way you can increase the efficiency of the nanaogenerators in lighter vehicles?

Our design is not optimized at this point. We have shown that the electric output increases with the weight applied to the wheel, i.e. the weight of the vehicle. It is intuitive to think that the electric output increases follows the frication. There are definitely room for further improvement of the efficiency. For example, the size of the electrode, the position of electrode, the electric property of the tire surface. We don’t know their contributions to the efficiency yet, but we are working on the optimization right now.

How do you see this technology progressing over the next few years?

This technology requires redesigning the tire structure in order to collect the electric current, which I don’t think is an easy task. But if we or other researchers can show that this technology can save high enough energy, this technology may soon be tested in real vehicle systems. Investment, tire engineers, electric engineers are all necessary component for the further progressing of this technology.

Where can our readers learn more about your work?

All of our research is introduced on our group webpage nanoscience.engr.wisc.edu/

About Dr. Xudong Wang

Dr. Xudong Wang is an associate professor in the department of Materials Science and Engineering at University of Wisconsin – Madison. He received his PhD degree from the school of Materials Science and Engineering at Georgia Institute of Technology in 2005. His current research interests include studying the nanometer scale piezoelectric properties; understanding the coupling effect between piezoelectric polarization and semiconductor functionalities; and investigating the growth mechanisms and developing assembly techniques of nanostructures for mechanical and solar energy harvesting. He has published more than 80 peer reviewed papers, which have been cited over 6,000 times and his current h-index is 36. He is also the recipient of NSF CAREER Award, DARPA Young Faculty Award, 3M Non-Tenured Faculty Award, Ross Coffin Purdy Award, and Technology Review Young Innovators Under 35 Award.